Week 40 (Sep 30-Oct 6)
High pressure is established again over Greenland, at least for a few days. At the same time, some low-pressure activity in the Atlantic and cream on the moss also has residual tropical hurricanes (Lorenzo) entering the western wind belt and will in some way affect the details of the weather over Europe. However, the big brushstrokes for week 40 feel clear.
Northern Europe generally receives unstable and chilly autumn weather, with passing rainstorms or areas with rain showers. In northern Scandinavia and Finland, it can potentially draw cold air from the Arctic Ocean, which will probably cause snow instead. Exactly how much of northern Scandinavia and northern Finland can receive snow remains to be seen.
Southwestern Europe is strongly influenced by the Azorean high pressure from the west, which provides hot and dry weather in Spain, Portugal and southern France. The British Isles and Central Europe end up in the border zone between the cool air in the north and the warm air in the south, which brings rain on and off. The rain is likely to be associated with smaller but intense low pressures, which also results in windy weather - at least on one occasion. Around Italy and the Balkans first warm, but then rain and much cooler. Possibly the drier and warmer weather will come back towards the end of the week again. Some bursts could also find their way down to the Middle East as well.
Week 41 (October 7-13)
The unstable weather over northern Europe continues, but the coldest air seems to be pushed away from northern Scandinavia and northern Finland. Still some rainy weather passing, perhaps with snowfall in the northernmost parts. However, it seems to be a bit drier over some areas as a whole, but exactly where is too early to say.
Central Europe seems to be getting some drier weather afterwards and any day of autumn heat feels likely. It is possible that the warmer air could temporarily slip up over southern Scandinavia as well, since the entire air mass package over Europe is expected to move north. Despite this, we cannot currently expect any British summer. Around the Mediterranean generally varying weather with some scrub areas here and there - probably even in the Middle East. Surprisingly, it seems to be in southern Spain and southern Portugal.
Week 42-43 (unspecified dates)
At least part of week 42 probably follows the same pattern as week 41, but then there is a clearer tendency to change. High pressure builds up over Scandinavia, which means much calmer weather over northern Europe. It also means a lot of clouds, sometimes with haze or fog that is difficult to light. The low pressures end up on a southerly path, which gives some rain over Western Europe, including Spain and Portugal. Around the eastern Mediterranean and in south-eastern Europe periodically warmer air can be found a bit north and the high-pressure influence there gives quite dry weather - though not completely scrubby.
Temperature contrasts around the Middle East and any shorter heat waves that give way can sometimes give some strong showers there.
Week 44-45 (Around the end of the month)
Given that high pressure is formed over Scandinavia, the next step will be absolutely decisive for where we end up at the end of the month. However, there is a certain probability that the high pressure will move west and / or north. In this case, it gives cold air from the north or northeast to look down over northern Europe. It could also open up for a first real snowfall over southern Scandinavia sometime during the period (which extends over the autumn holidays and the Halloween weekend).
With the present scenario, most of central and southern Europe receives unstable weather, while the eastern Mediterranean and the Middle East receive warm and dry weather for the season. Another alternative is that a larger low pressure is formed over western Russia. This development is likely if the Scandinavian high pressure is shifted straight to the west. In such a situation, the forecast does not change significantly for northern Europe, but for southeastern Europe and the Middle East the difference can be large. The cold air from the north can be pushed far south with north winds, which risks causing quite extensive rainfall when it meets the hot air.